The invention furthermore relates to a refrigeration system comprising such an electronic expansion valve.
The invention furthermore relates to a method for calibrating an electronic expansion valve comprising an inlet, an outlet, an armature, a stop member, a biasing member and a solenoid coil, wherein the biasing member provides a biasing force on the armature towards a closing direction to stop a fluid flow from the inlet to the outlet, and wherein the solenoid coil provides a magnetic force on the armature towards an opening direction to allow a fluid flow from the inlet to the outlet if a solenoid coil is provided with an electric current.
Electronic expansion valves are a common component of refrigeration or air conditioning systems. A basic refrigeration cycle contains a compressor, a condenser, an expansion valve (for example an electronic expansion valve) and an evaporator. In the usually closed cycle a refrigerant is first introduced into the compressor as a low temperature, low pressure gas. The compressor compresses the refrigerant to a high temperature, high pressure gas that is guided to the condenser. In the condenser, the high temperature, high pressure gas condenses to a high pressure liquid form of the refrigerant, whereby heat is transferred to the ambient environment.
Note that some refrigerants like CO2 may not condense in the condenser depending on the pressure and the external temperature. In this case the condenser may be operated as a gas cooler.
The high pressure fluid then arrives at the expansion valve, that limits the flow of fluid to the subsequently arranged evaporator. The expansion valve limits the flow such that the pressure of the fluid in the evaporator stays low and thereby allows the fluid to evaporate back to the gaseous phase, thereby absorbing heat from the ambient environment.
Consequently, it is critical for the effectiveness of the refrigeration cycle that the flow of the fluid through the expansion valve to the evaporator can be controlled with a high precision. To this end, it is for example known to use temperature or pressure sensors to adjust the opening or closing cycles of the expansion valve accordingly.
Afterwards, the low pressure gas exits the evaporator and is fed back into the compressor whereby the refrigeration cycle starts anew.
An electronic expansion valve of the kind mentioned at the outside as well as a corresponding refrigeration system is, for example, known from U.S. Pat. No. 6,374,624 B1. The expansion valve disclosed therein comprises a cylindrical armature that is urged towards a stop member by a spring force of a spring in the direction towards the outlet of the expansion valve. The expansion valve furthermore comprises a fixed core that additionally acts as a flow restrictor. By activating the solenoid coil a magnetic force acts upon the armature, moving the armature away from the stop member thereby opening the expansion valve against the force of the spring as well as the force of the differential fluid pressure. Such a solution has the disadvantage that in order to allow the expansion valve to open even at a large pressure difference between the inlet and the outlet, the magnetic force provided by the solenoid coil on the armature must be chosen rather large. Consequently, the expansion valve may only be controlled between a completely closed and a completely open position.
A further electronic expansion valve is known from JP H1089523. In this case a spring force urges the armature towards an opening position of the electronic expansion valve in case the solenoid coil is not provided with a current. When activating the solenoid coil the armature is displaced by the magnetic force towards the inlet. Depending on the strength of the current and the resulting magnetic force the armature may close one or several fluid paths in a nozzle, thereby reducing the fluid flow through the valve. The electronic expansion valve may however not be fully closed as a central orifice will remain open even at full displacement of the armature.
This solution allows for a more precise control of the fluid flow within a certain range, it does however not permit to fully close the valve. Consequently, the applications are limited.